The present invention provides a new process of fabricating a single crystal silicon MEM tunneling devices using low-cost bulk micromachining techniques while providing the advantages of surface micromachining. The prior art, in terms of surface micromachining, uses e-beam evaporated metal that is patterned on a silicon dioxide (SiO2) layer to form the control, self-test, and tip electrodes of a tunneling MEM switch or sensor. A cantilevered beam is then formed over the electrodes using a sacrificial resist layer, a plating seed layer, a resist mold, and metal electroplating. Finally, the sacrificial layer is removed using a series of chemical etchants. The prior art for bulk micromachining has utilized either mechanical pins and/or epoxy for the assembly of multi-Si wafer stacks, a multi-Si wafer stack using metal-to-metal bonding and an active sandwiched membrane of silicon nitride and metal, or a dissolved wafer process on quartz substrates (Si-on-quartz) using anodic bonding. None of these bulk micromachining processes allow one to fabricate a single crystal Si cantilever (with no deposited layers over broad areas on the beam which can produce thermally mismatched expansion coefficients) above a set of tunneling electrodes on a Si substrate and also electrically connect the cantilever to pads located on the substrate and at the same time affording good structural stability. The fabrication techniques described herein provide these capabilities in addition to providing a low temperature process so that CMOS circuitry can be fabricated in the Si substrate before the MEMS switches and/or sensors are added. Finally, the use of single crystal Si for the cantilever provides for improved process reproductibility for controlling the stress and device geometry. A protrusion is formed on at least one of the substrates to provide better mechanical stability to the resulting switch or sensor.
Tunneling switches and sensors may be used in various military, navigation, automotive, and space applications. Space applications include satellite stabilization in which MEM switch and sensor technology can significantly reduce the cost, power, and weight of the presently used gyro systems. Automotive air bag deployment, ride control, and anti-lock brake systems provide other applications for MEM switches and sensors. Military applications include high dynamic range accelerometers and low drift gyros.
MEM switches and sensors are rather similar to each other. The differences between MEM switches and MEM sensors will be clear in the detailed disclosure of the invention.